Markings on bus floors

[37351ml]

Does anyone know what the markings inscribed on bus floors signify. For example wa1892 has some marked in yellow on the floor beneath the cash vault : "W Tu". Many of walsall's e200s have them too.presumably the engineers write them to identify any repairs required?

[Tony]

It's something Walsall cleaners do to show that bus has been cleaned that night so their colleagues don't waste time checking. Tu-Tuesday etc